Faster Grunt copy task

copy.js

import {unique} from 'lodash';
import * as path from 'path';

/*
 * Grunt copy task that's faster by eliminating unnecessary or redundant fs calls.
 *
 * Things it does *not* do:
 * - set or copy file mode / permissions
 * - "process"ing files
 * - "process"ing files as raw buffers
 * - recursively copying directories
 * - tally created files and directories identically to grunt-contrib-copy
 * - verbose logging identical to grunt-contrib-copy
 * - catch case where src is directory and dest is a pre-existing file (silently succeeds instead)
 */
grunt.registerMultiTask('copy', function() {
    const {target, data, files} = this;
    const destFiles = [];
    files.forEach(fileMapping => {
        const {src: srcArray, dest} = fileMapping;
        if(srcArray.length !== 1) throw new Error('Only supports one-to-one file mappings.');
        destFiles.push(dest);
    });
    const dirs = unique(destFiles.map(f => path.dirname(f)));
    addAllParentDirs(dirs);
    // Ensure that parent directories are always created before children
    dirs.sort();
    let createdDirectories = 0;
    dirs.forEach(dir => {
        if(mkDir(dir)) createdDirectories++;
    });
    let copiedFiles = 0;
    files.forEach(({src: [src], dest}) => {
        switch(copyFile(src, dest, true)) {
            case 1:
                copiedFiles++;
                break;
            case 2:
                createdDirectories++;
                break;
        }
    });
    console.log(`Created ${ createdDirectories } directories, copied ${ copiedFiles } files`);
});


/**
 * Given an array of paths, recursively adds paths to all containing directories.
 * For example, for path '/foo/bar/baz', adds '/foo/bar' and '/foo'.
 */
function addAllParentDirs(dirs) {
    for(let i = 0; i < dirs.length; i++) {
        const dir = dirs[i];
        const dirOfDir = path.dirname(dir);
        if(dirOfDir !== '.' && dirs.indexOf(dirOfDir) === -1) dirs.push(dirOfDir);
    }
}


/**
 * Copies src to dest.  If src is a directory, then creates target directory.
 * Returns 0 if nothing was done, 1 if file was created, 2 if directory was created.
 */
function copyFile(src, dest, createDir = false) {
    let content;
    try {
        content = fs.readFileSync(src);
    } catch(e) {
        // If we tried to read a directory, that's ok.  Just skip it.
        if(e.code === 'EISDIR') {
            if(createDir && mkDir(dest)) return 2;
            return 0;
        }
        throw e;
    }
    fs.writeFileSync(dest, content);
    return 1;
}


/**
 * Create directory at given path if a file or directory does not already exist at that path.
 * Does not indicate if a file existed at that path even though that might be unexpected.
 * Returns true if directory was created, false otherwise.
 */
function mkDir(dir) {
    try {
        fs.mkdirSync(dir);
    } catch(e) {
        // If the directory already exists, that's ok.
        if(e.code !== 'EEXIST') throw e;
        return false;
    }
    return true;
}